The present invention is directed toward lifting tongs for use with a crane and more particularly toward such lifting tongs which have adjustable and interchangeable jaws so that the same can be used to lift various different materials of different sizes.
Various lifting tongs for lifting I-beams and the like have been proposed in the past. These are shown, for example, in U.S. Pat. Nos. 3,201,167 and 3,572,808. In each of these patents, the claws include jaws which fit around the edges of the top flange of the I-beam. These would appear to function properly for a particular size I-beam. However, for different size I-beams having different widths or thicknesses of the upper flange, the known tongs will not grip properly which can create a seriously dangerous situation.
The prior art also suffers from another serious defect. Insofar as Applicant is aware, all prior art lifting tongs are specifically designed for a particular application. There are no devices known to applicant which are adaptable to numerous different applications for lifting various different types of materials. This, of course, significantly increases capital costs since a contractor, builder or similar business would have to own numerous different lifting tongs.